PDF Publication Title:
Text from PDF Page: 104
68 Handbook on the Physics and Chemistry of Rare Earths FIG. 65 c a Cl MgO4 Ca2 Ca1 SiO4 (disordering) b Crystal structures of Ca8Mg(SiO4)4Cl2. Picture was drawn based on the structure data obtained from the database (ICSD #68243). stability; in particular, Eu2+-activated Ca8Mg(SiO4)4Cl2 have been demon- strated to be high efficient green-emitting phosphors for near-UV and blue- LED-based white LEDs (Guo et al., 2011a; Koo et al., 2008; Li et al., 2013; Lin et al., 2002; Zhang and Liu, 1992). The structure of Ca8Mg(SiO4)4Cl2 is cubic with space group Fd3m and a1⁄41.506 nm. There are three kinds of cation sites with different crystallographic environments: two Ca2+ sites (Ca1 and Ca2) and one Mg2+ site (Fig. 65). The site for Ca1 (C2v symmetry) adopts six- fold oxygen coordination with additional capping by the next nearest six Cl at a distance of approximately 0.5 nm. Whereas, the site of Ca2 (C1 symmetry) adopts eightfold coordination with six oxygen and two chlorine. The site ratio of Ca1:Ca2 in the structure is 1:3. In addition, Mg2+ occupies a tetrahedral position with four O2 at the identical distance of 0.186 nm. The excitation spectrum of the phosphor involves a broad absorption band from 280 to 480 nm, covering near-UV and blue light region (Fig. 66). In the emission spectrum under excitation at 330 nm, there are obviously two emis- sion bands with peaks at 425 and 503 nm. In view of the crystal-field strength of each Ca2+ site, the emission bands at around 425 and 505 nm originate from Eu2+ substituting for Ca1 and Ca2 site, respectively (Lei et al., 2010; Wang et al., 2007; Zhang and Liu, 1992). When excited at 440 nm, the inten- sity of the green emission (503 nm) measured at 150°C is 64% of that measured at 25°C (Li et al., 2013). 4.4.1.2 Sr3Al2O5Cl2:Eu2+ Phosphors Detailed crystallographic data for Sr3Al2O5Cl2 are only available from the study by Leib and M€uller-Buschbaum (1986). According to this study, Sr3Al2O5Cl2 crystallizes in an orthorhombic structure with space group P212121, a 1⁄4 b 1⁄4 c 1⁄4 0.9422 nm and V 1⁄4 0.8364 nm3. Surprisingly, the lattice parameters apparently belong to a cubic system in spite of the orthorhombic system reported. The reported space group seems to be wrong, and the cubic spacePDF Image | HANDBOOK ON THE PHYSICS AND CHEMISTRY OF RARE EARTHS
PDF Search Title:
HANDBOOK ON THE PHYSICS AND CHEMISTRY OF RARE EARTHSOriginal File Name Searched:
Chemistry-Rare-Earths-49.pdfDIY PDF Search: Google It | Yahoo | Bing
Sulfur Deposition on Carbon Nanofibers using Supercritical CO2 Sulfur Deposition on Carbon Nanofibers using Supercritical CO2. Gamma sulfur also known as mother of pearl sulfur and nacreous sulfur... More Info
CO2 Organic Rankine Cycle Experimenter Platform The supercritical CO2 phase change system is both a heat pump and organic rankine cycle which can be used for those purposes and as a supercritical extractor for advanced subcritical and supercritical extraction technology. Uses include producing nanoparticles, precious metal CO2 extraction, lithium battery recycling, and other applications... More Info
CONTACT TEL: 608-238-6001 Email: greg@infinityturbine.com (Standard Web Page)